"Ultracold atomic gases are quantum systems with an extraordinary degree of experimental control. They allow us to unveil fundamental aspects of many body physics in the realm of quantum mechanics with unprecedented precision.
We worked with ultracold spinor Bose gases —atomic quantum systems with spin degree of freedom— to investigate the origins of magnetism in materials. A general understanding the nature of magnetic quantum phases of matter requires the study of magnetic systems —beyond electronic spin-1/2 systems— where more magnetic phases are possible. Therefore, we studied a sample of optically trapped ultracold sodium atoms, a physical realization of a gas of spin 1 particles with antiferromagnetic interactions.
The scientific objectives of the action are (i.) understand quantum phase transitions in a 1D spin-1 system with and without a lattice; (ii.) investigate out-of-equilibrium systems across a quantum phase transition; and (iii.) investigate spin-orbit coupling (SOC) in 1D spinor gases.
We studied magnetic phases in a spin-1 system where the atoms can populate any quantum superposition of the three components mF=+1,0,-1, in a reduced dimensionality (1D). We measured the magnetic phase diagram as a function of an external magnetic field B, and observed the formation of magnetic domains within the sample. At low B, the system forms a mF = ±1 mixture favored by antiferromagnetic interactions. At high B, the system evolves into a mF = 0,+1 phase separated state, energetically favored due to the quadratic Zeeman effect. In contrast to earlier work, we took special care to cancel external magnetic forces that would have influenced the formation and spatial arrangement of the domains.
We also investigated the linear response of phase separated magnetic domains to an external magnetic force. We found that the response of an antiferromagnetic spin-1 BEC was significantly larger than that for single atoms. This ""enhanced Zeeman effect"" arises from the interplay between atomic interactions and bosonic statistics.
Finally, we studied the out-of-equilibrium response of magnetic domains to an external magnetic force.
CONCLUSION
This MSCA fellowship, part of the Career Restart panel, allowed Karina Jiménez García to reincorporate to research after a maternity leave period. She successfully integrated in the existing group and resumed her research.
The Spin1D project realized at Laboratoire Kastler Brossel (LKB) in Paris aimed at addressing fundamental aspects of quantum magnetism, by performing experiments based on sample of ultracold spin-1 atoms with antiferromagnetic interactions in a 1D geometry.
The most relevant achievements are: 1) the implementation of a 1D optical trap for cold atoms; 2) the observation of a quantum phase transition in a spin-1 ultracold atom system; 3) the observation and characterization of spin domains in 1D; 4) the study out-of-equilibrium dynamics; and 5) the characterization of the enhanced response to a magnetic force.
The host laboratory obtained a great amount of knowledge from the work led by Karina during the fellowship. The laboratory will continue to pursue state-of-the-art experiments using this spinor system.
Karina’s performance during the development of the fellowship granted her a research position at Centro de Investigación y de Estudios Avanzados del IPN - Unidad Querétaro, Querétaro, in México, her home country."
